I first found this story about 25 years ago. I since lost it, but managed to scour the internet and piece together most of the chapters. However, there are still a few that I am missing. The story was called New Neighbours, and was originally hosted on Butterfly BBS (long dead.) I believe I had 11 chapters before I lost it, I have located chapters 1-8, would love to find the rest of it. The gist of the story is that Jimmy and Dana move in to a (unbeknownst to them) swinging apartment complex, and meet their friendly neighbors Mike and Barbara, who indoctrinate them into the culture.